1. Field of the Invention
The present invention relates to a system for drawing patterns of LSI, etc., directly on a substrate such as a wafer, etc., having an orientation flat and adjusting marks, by using a charged particle beam such as an electron beam having a rectangular cross-section, etc.
2. Description of the Related Art
Heretofore, in a variably-shaped-electron-beam lithography system for drawing a pattern on a wafer having an orientation flat and adjusting marks, the direction of the orientation flat is made to coincide with the X or Y direction of the X-Y movement of a sample table within about 5 to 10 mrad, and thereafter the direction is determined by using the adjusting marks by means of a prealigner within about 1 mrad (JP-A-Hei 2-202012). The prealigner may be located either in a sample chamber or outside thereof, but in all cases the construction is complicated.
The reason why a high-precision prealignment is required will be explained, referring to FIG. 2. If the prealigned state is bad, e.g. if the orientation flat is rotated by .theta. radians with respect to the moving direction of the stage, as indicated in FIG. 2, chips positioned on the wafer are rotated also by .theta.. It is easy to rotate the deflection direction of the electron beam used for the drawing by .theta. by detecting the adjusting marks to effect adjusting correction. This was effected heretofore.
However, since the shaped beam itself was not rotated, e.g. in the case where a line was drawn by using the shaped beam, there was a problem that the line was drawn stepwise, as indicated in FIG. 3. That is, supposing that the greatest dimension, of the shaped beam is .iota. .mu.m, the deviation .DELTA..iota. between two adjacent shots due to the shaped beam is equal to .iota..times..DELTA..theta..
Now, supposing that .iota.=10 .mu.m and .theta.=5 mrad, .DELTA..iota.=0.05 .mu.m. The pattern of different shots exposed on a photosensitive resin is stepwise, as indicated in FIG. 3. In order that this stepwise pattern on the photosensitive resin be invisible, .DELTA..iota.&lt;0.01 .mu.m is necessary. Consequently it was necessary to carry out the prealignment so that .theta. is smaller than 1 mrad.
As described above, since prealignment work was necessary for the prior art system, extra devices and extra work were required. Concretely speaking, as one of the extra devices it can be cited that the wafer stage had a rotation adjusting function, in the case where the rotational angle was great. In this way the construction of the stage was very complicated, which could produce worsening in vacuum, sticking of dust on the wafer, trouble, and lowering in the drawing precision. Additionally, the system was expensive due to its complexity. Further, in the case where it was difficult to dispose the rotating function on the stage, the wafer rotation adjusting function was disposed within an external prealigner. Also, in this case, a problem similar to that described above took place.